And veteran left-winger John McDonnell reiterated his call for British troops to be withdrawn from Afghanistan - challenging his rivals to adopt his stance.

Their comments came as former Labour leader Lord Kinnock came out in support of Ed Miliband, while David Miliband enjoyed a massive lead among voters in a newspaper poll.

Along with former schools secretary Ed Balls, the four MPs are battling to be elected Labour leader in September.

A YouGov survey for The Sunday Times showed David Miliband has 23% support among voters but surprisingly put Ms Abbott in second place on 9%, with Ed Miliband on 8%, Mr Balls 6%, Mr Burnham 4%, and Mr McDonnell 2%.

Ms Abbott told Sky News Sunday Live the poll was evidence that the public was taking her candidacy "very seriously indeed".

Insisting that she was "running to win", she said: "I do think it is important that the group of candidates that debate the leadership over the summer actually represent the Labour Party as it is in 2010.

Ms Abbott said she wanted Labour to recapture ground on civil liberties, discuss the balance of tax rises and spending cuts to fill the nation's financial black hole and question whether the UK should be in Afghanistan.